Summary

Detraining (short-term <4 weeks)

Strength can be maintained without training up to 3-4 weeks, but is gradually lost thereafter (strictly speaking, you can temporarily lose strength before this, but it comes back so quickly during retraining that it doesn’t matter)

Muscles start to atrophy after 2-3 weeks, though gains usually come back quickly, at least in beginners.

Endurance performance decreases by 4 to 25% after 3-4 weeks.

VO2 max declines by 6 to 20% in highly trained athletes at around 4 weeks of detraining.

Beginners can maintain endurance performance for at least 2 weeks without training, though recent VO2max gains can be reversed after 4 weeks.

You look smaller during the first weeks of detraining because muscle glycogen stores shrink, not because you lose mass (though, the muscles literally become smaller because glycogen binds water). Good news: the effect is temporary since glycogen stores quickly expand when you resume training.

Flexibility is reduced after 4 weeks of detraining by ~7-30%

Bed rest/immobilization speeds up muscle atrophy

Maintaining gains

To maintain strength during 4+ weeks of detraining, train at least once per week (for beginners). Trained lifters could maintain strength gains with eccentric training.

To maintain hypertrophy during 4+ weeks of detraining, train at least once per week (for beginners). There’s not much long-term data for trained lifters, but eccentric training could help.

To maintain endurance during 4+ weeks of detraining, you can lower training volume by 60 to 90%, training frequency by no more than 20-30% in athletes but beginners can reduce it by 50 to 70%. Training intensity should be the same.

If injured, use alternative training forms such as strength training (which can maintain some endurance performance) or underwater running.

It’s easier to regain strength and muscle mass once it’s lost because of muscle memory (myonuclei and neural adaptations).

Newsletter

Sign up to get notified about new content. You will receive monthly updates.

Name (optional)

Email

Introduction

Sometimes life happens and we are unable to train for one or two weeks. Other times, we become injured or sick so that we take extended breaks from training. If this has happened to you, it’s inevitable that you start to wonder when you will lose your progress. Some people start to worry after two days, while others worry after two weeks. In this article, I will answer how detraining affects strength, muscle size, and endurance.

The figure shows how 1RM changes over the course of 24 weeks of training. The black lines (PTR group) trained for 6 weeks, then took a break for 3 weeks (rinse and repeat). The white line (CTR group) trained continuously. By the end there was little difference in maximum strength between groups. Figure by Ogasawara et al. (2013).

A study by Costa et al. (2016) found that 1RM leg extension strength remained high above baseline during 2 weeks of detraining. The interesting twist here is that the participants only trained their leg one week (3 sessions) before detraining. So they barely got one good week of training done. And still the strength is almost unchanged two weeks later:

At this point in time, I won’t speculate and try to answer these questions, but I do think the data is very interesting. I will write an in-depth review on periodization in the future (I have 60+ studies on this topic!).

Trained lifters

There is much more data on trained lifters. For this section I will mainly cite one systematic review by McMaster et al., (2013). The review analyses 27 studies to determine what the ideal frequency, volume, etc. for strength gains in rugby players. They also examine detraining and how it affects strength. The participants had the following characteristics:

“‘Highly trained’ athletes are those whom have been resistance training for 3 plus years and are currently participating in collegiate level, state level, semi-professional and professional sport [37]. Studies utilizing these elite athletic populations were included in this review, all others were excluded.”

So we are talking about trained athletes. Here’s what they found regarding detraining and strength:

"Based on the above outcomes and past literature, [ 9, 10, 12, 17, 29, 42, 58, 60, 63, 84] it can be speculated that maximum strength levels can be maintained for up to 3 weeks without resistance training, but decay rates will increase thereafter (5–16 weeks).”

This is the best evidence we have for now when it comes to trained lifters and detraining. The conclusion is also supported by another review which concludes:

“Strength performance in general is (...) readily retained for up to 4 wk of inactivity, but highly trained athletes’ eccentric force and sport-specific power may suffer significant declines.” (Mujika and Padilla, 2001).

Update: A study from 2017 finds that trained men retain strength and muscle mass during a 2 week period of detraining (Hwang et al., 2017)

When researchers measure gains, they will look at things like Fat-Free Mass (FFM), Lean Body Mass (LBM), or Fiber Cross Sectional Area (CSA). They will do this by using tools like DXA, BIA, MRI, or muscle biopsy. Now, these measurements are useful, but they are also affected by how much glycogen we store in our muscles (Bone et al., 2016). So when muscle glycogen stores shrink during detraining, we “lose” muscle mass, or more accurately, the water contents of our muscles decreases (Nygren et al., 2001). On the flipside, you could even "trick" body estimates by going on a high carb diet to glycogen load your muscles (Rouillier et al., 2015; Bone et al., 2016). On the flipside, going low-carb or on a cut can lower your glycogen and water stores. This affects "muscle mass" (Hulmi et al., 2016)

This is why we have to take the atrophy and hypertrophy studies with a grain of salt. When beginners start exercising, their muscle glycogen stores will grow quickly and they will retain more water, as shown below:

What 16 weeks of strength training does for total body water in beginners. Figure by Ribero et al., 2014

If researchers were to measure gains after a couple weeks of training, it could simply be increased muscle glycogen. On the other hand, if researchers are using tools that can detect water changes within our bodies, then they can measure “real” muscle protein gains much better (LaForgia et al., 1999; Mallinson et al., 2011). Indeed, a study found that endurance athletes lost muscle mass during a 3-week detraining period (LaForgia et al., 1999). However, the muscle mass loss was only found using measurement tools that weren’t ideal for the job (2 and 3 compartment models). Check out a comparison of the models below:

Luckily, the same researchers also measured water mass using a 4 compartment model. They found that the 0.7 kg loss of lean mass was actually a loss of 0.7 kg total body water. Hence, the detrained athletes didn’t lose any muscle mass during a three week break from training (LaForgia et al., 1999). But, their muscle glycogen stores did shrink.

The figure shows how CSA [hypertrophy] changes over the course of 24 weeks of training. The black lines (PTR group) trained for 6 weeks, then took a break for 3 weeks (rinse and repeat). The white line (CTR group) trained continuously. By the end there was little change in gains. Note that the CTR group did a lot more volume because they never took a break: “the PTR group had 25 % fewer training sessions”. Figure by Ogasawara et al., 2013.

My bet is that muscle glycogen stores shrunk during the detraining phases, and rebounded during the training phases. Therefore, we are, to some extent, observing changes in muscle glycogen, not muscle mass. Though I don’t know exactly how much of the gains are glycogen gains compared to “dry” muscle protein gains (the researchers didn’t control for body water). As you can see, the continuous group (CTR) made huge gains the first 6-9 weeks of training and then the curve becomes much flatter. I think this is because they made both muscle protein gains and glycogen gains. Once the "wet" glycogen/water gains wear off, we are left with dry gains.

Though I will write a counterpoint: Muscles can contain a maximum of 4g glycogen per 100g wet muscle (Hansen, 1999). Glycogen can bind 3g of water per gram (Ribero et al., 2014). So the maximum amount of glycogen + its bound water is: 4g + 4*3g = 4g + 12g = 16g (per 100g muscle).

The final answer is 16% (shoutout to Greg Nuckols for writing about this 2015). This shows us that glycogen and its bound water can’t make up huge changes in gains. But, it would explain small changes in muscle mass during detraining (for example a loss of 5-6% CSA as some studies have suggested (Hortobágyi et al., 1993; Ogasawara et al., 2013). When it comes to filling muscles with glycogen, one study found that glycogen loading lead to a 3,5% CSA increase in untrained people (Nygren et al., 2001) while another study detected a 2-3% FFM increase in well-trained cyclists (Bone et al., 2016). Perhaps glycogen loading/depletion plays an even bigger “hypertrophic” role in people who have at least 10-16 weeks of resistance training experience?

Glycogen reduction following detraining would also explain, along with other factors, why it initially feels a bit more difficult to use the same volume in strength or endurance exercise as you trained with before the break (Knuiman et al., 2015).

Trained lifters

Though a question remains, when do muscles of trained lifters start to atrophy? According to a review by Fisher et al., 2013:

I looked through the studies they cite and it’s true that beginners could take 3 week breaks from training without losing mass. A different study that looks at trained powerlifters with ~8+ years of experience, found that their type II muscle fibers became ~6% smaller after a two week gym break. Though, their body weight didn’t change (Hortobágyi et al., 1993). I think it’s fair to say the “atrophy” was due to glycogen loss, as we discussed previously. A study from 2017 finds that trained men retain strength and muscle mass during a 2 week period of detraining (Hwang et al., 2017). Hence, it seems like trained lifters can take a 2-3 week break from the gym without losing gains.

I should mention that there is individual genetic/epigenetic variation to muscle hypertrophy and atrophy (Fisher et al., 2013), so it’s hard to give any absolute cut-off point. We don’t know for sure when individuals start to lose muscle mass. We have a better idea of when groups of people start to lose mass, on average. Even so, it does seem like complete bed rest (or limb immobilization) accelerates muscle loss compared to a gym break where you move around and do everyday activities (Hortobágyi et al., 2000; Dirks et al., 2016; Rudrappa et al., 2016; Cholewa et al., 2017).

This indicates that a break from the gym shouldn’t include a break from movement and activity in general. It’s possible that a break leads to quicker atrophy if you’re highly sedentary. Maybe partaking in light activity maintains gains for longer? We will look at this in the next main section.

If I don’t lose muscle after 2-3 weeks of detraining then why do I look smaller?

When do you lose endurance capacity?

There are many ways to figure out our endurance endurance capacity and endurance performance. One of the most standard measurements is VO2max, but there are other ways as well, like heart rate variability, or time to exhaustion (how long you can run, cycle, etc. before you have to stop) . Though VO2max doesn't necessarily tell us the whole story of endurance capacity:

"Aerobic endurance is independent from VO2max , since two individuals with the same VO2max are not necessarily able to sustain the same fraction of VO2max for a given effort duration" (Bosquet and Mujika, 2012)

Though things change if you’re either injured, sick, or perhaps you’re very busy for a couple of months so you just don’t have the time to hit the gym 3-5 times a week. In that case, there are good news; you can maintain gains and strength with a much lower overall volume, and frequency.

Strength maintenance

In beginners, strength can be maintained (and even increased!) with volumes from 1/3rd all the way down to 1/9th of previous training volumes (Bickel et al., 2011). Beginners can even take multiple breaks (3 weeks) from training and still increase their strength gains at an impressive rate (Ogasawara et al., 2013). It seems like training once a week is enough to maintain gains over a period of 8-12 weeks (Rønnestad et al., 2011; Tavares et al., 2017), and perhaps even longer .

Trained lifters might want to include eccentric training into their programs before and during a period of lowered training volumes/frequencies. Eccentric movements might help retain strength for longer (Mujika and Padilla, 2000a; Coratella and Schena, 2016). If you are injured in one limb, you might want to take advantage of the cross-training effect. For example, the body increases neural adaptations (strength) in both arms even if you only train one side (Mujika and Padilla, 2000a). This might be important if you need to keep your arm/leg in a caste for a month or so. Though it’s probably not a good idea to train only one side of the body for long periods of time, due to long-term muscle mass and strength imbalances.

Muscle mass maintenance

In beginners, muscle mass can be maintained with volumes all the way down to 1/9th of previous training volumes (Bickel et al., 2011). Though, it’s generally better for gains to use at least 1/3rd of previous training volumes:

As we discussed previously, it’s also possible for beginners to take multiple breaks (3 weeks) from training and still increase their CSA gains at an impressive rate (Ogasawara et al., 2013). One study suggests beginners can maintain muscle gains for 8 weeks, only training once per week (Tavares et al., 2017)

It looks like beginners have less to lose and more to gain, no matter what they do. Sadly, I don’t have much data on trained lifters and long-term hypertrophy maintenance. Even so here’s one quote (it refers to cardio but I think the core message applies to hypertrophy as well):

“it would seem worthwhile for the injured or less active athlete to perform either a reduced training programme or an alternative form of training (i.e. to cross-train), in an attempt to avoid or reduce detraining.” (Mujika and Padilla, 2000a)

Maintaining endurance

Once we start taking longer breaks from endurance training, i.e. 5 weeks, our cardio "gains" quickly diminish (Maldonado-Martin, 2016). Though, there are ways to prevent this. Several research teams now advise athletes to keep training during the off-season, or if they are injured (Joo, 2016; Maldonado-Martin, 2016). Here are some ways to maintain endurance capacity during breaks from regular training:

If injured, such as Achilles tendinosis or ankle sprain, use alternative training methods such as underwater running, cycling, or perhaps rowing (Bosquet and Mujika, 2012)

“Several studies have indicated that the maintenance of training intensity during periods of reduced training and taper (...) is of paramount importance in order to keep training-induced physiological and performance adaptations. [59,64,68-74] On the other hand, training volume can be reduced to a great extent without falling into detraining. This reduction can reach 60 to 90% of previous weekly volume, depending on the duration of the reduced training period, both in highly trained athletes and recently trained individuals. [28,29,57-60,63,69-8]”

“Finally, reports from the literature indicate that training-induced adaptations are readily maintained for several weeks during periods of reduced training frequencies, but the reductions should be more moderate in athletes (no more than 20 to 30%) than in recently and moderately trained individuals (up to 50 to 70%)." (Mujika and Padilla, 2000a)

How are myonuclei relevant to detraining?

Once you become trained and have gathered extra myonuclei, you’d want to keep them throughout detraining. The good news is that myonuclei seem to stay in muscles, even when detrained for long periods of time (Gundersen, 2016). Myonuclei might remain for 15 years or more in human muscles (Gundersen, 2016). This phenomenon has been called “muscle memory”, because the muscles seem to remember their former glory (Gundersen, 2016). The idea is that you can quickly return to previous training levels and regain muscle size if you’ve been highly trained before. Though, most studies on muscle memory and performance are done on animals (Bruusgaard and Gundersen, 2008; Bruusgaard et al., 2010; Egner et al., 2013). There are some studies that look at muscle memory during detraining and retraining in humans, but they are low quality (Staron et al., 1991).

Steroid users seem to have more myonuclei (Kadi et al., 2000; Yu et al., 2014), and the myonuclei could remain in their muscles for a long time. This has implications for banning steroid users from sports; maybe bans should be longer due to the long-term advantage the extra myonuclei give users (Gundersen, 2016).

Other “comeback” mechanisms

Several studies show that the body can maintain muscle size and strength over periods of detraining. This could lead to quick gains after detraining, similarly to when you started training for the very first time (Bruusgaard et al., 2010; Fisher et al., 2013).

This isn’t necessarily because of anabolic resistance or myonuclei, because the study participants were beginners. But, the studies do suggest that there are mechanisms that make it easier to “come back” after 3 weeks detraining in beginners. Maybe the same happens in trained lifters?

Other effects of detraining

I added this section for those that are interested in the various technical aspects of detraining.

Flexibility

“It has been shown that 4 weeks of training cessation significantly lowered the flexibility of hip, trunk, shoulder and spine by 7.4 to 30.1% in male and female physical education students” (Mujika and Padilla, 2000)

Muscle characteristics

Cardiovascular characteristics

Metabolic characteristics

Conclusion

The evidence suggests that both trained athletes and beginners can maintain their strength, muscle, and endurance gains for at the very least 2-4 weeks without much training. During detraining, muscles carry less glycogen and water so they seem smaller. The good news is that it's relatively easy to maintain gains in short periods of time. Training volume and frequency can be reduced, but intensity should remain the same. The body also has various mechanisms it can use to "come back" from detraining quickly.